Field of the Invention
The present invention relates to mobile communication.
Related Art
3rd generation partnership project (3GPP) long term evolution (LTE) evolved from a universal mobile telecommunications system (UMTS) is introduced as the 3GPP release 8. The 3GPP LTE uses orthogonal frequency division multiple access (OFDMA) in a downlink, and uses single carrier-frequency division multiple access (SC-FDMA) in an uplink.
Such LTE may be divided into a frequency division duplex (FDD) type and a time division duplex (TDD) type.
As set forth in 3GPP TS 36.211 V10.4.0, the physical channels in 3GPP LTE may be classified into data channels such as PDSCH (physical downlink shared channel) and PUSCH (physical uplink shared channel) and control channels such as PDCCH (physical downlink control channel), PCFICH (physical control format indicator channel), PHICH (physical hybrid-ARQ indicator channel) and PUCCH (physical uplink control channel).
Meanwhile, as more and more communication devices require greater communication capacities, efficient use of a limited frequency band is highly demanded for a next-generation wireless communication system. Even for a cellular communication system such as an LTE system, using 2.4 GHz, an unlicensed band used by the existing WLAN system, and 5 GHz, which is also an unlicensed band, for traffic bypassing is considered. This is called LTE-U.
A base station of an LTE system has to perform Carrier Sensing (CS) in order to transmit data in the unlicensed band. However, a WLAN or any other communication node may not exist in a specific area at a specific time due to Cell planning, and even if the WLAN or any other communication node exist, its degree of interference may interfere the base station of the LTE system when the base station uses the unlicensed band for data transmission.
Nonetheless, performing CS always in the unlicensed band may be inefficient.